Polymer/polyol compositions suitable for use in producing polyurethane foams, elastomers and the like are known materials. The basic patents in this field are U.S. Pat. Nos. 3,304,273, 3,383,351, U.S. Pat. No. Re. 28,715 and U.S. Pat. No. Re. 29,118 to Stamberger. Such compositions can be produced by polymerizing one or more olefinically unsaturated monomers dissolved or dispersed in a polyol in the presence of a free radical catalyst. Many Examples in the Stamberger patents utilize various carboxylic acids in the monomer mixtures; and, more particularly, itaconic acid is used by itself and as a co-monomer present as a minor constituent based on the total weight of the monomer mixture. These polymer/polyol compositions have the valuable property of imparting to, for example, polyurethane foams and elastomers produced therefrom, higher load-bearing properties than are provided by unmodified polyols.
In addition, U.S. Pat. No. 3,523,093 to Stamberger discloses a method for preparing polyurethanes by reacting a polyisocyanate with a mixture of a polyol solvent medium and a preformed normally solid film-forming polymeric material obtained by polymerization of ethylenically unsaturated monomers. The film-forming polymer may be prepared by various techniques, including polymerizing the monomers in the presence of reactive radial-containing compounds such as alcohols and mercaptans.
The polymer/polyol compositions that found initial commercial acceptance were primarily compositions produced from polyols and acrylonitrile. Such compositions were somewhat higher in viscosity than desired in some applications. Further, such compositions were at least primarily used commercially in producing foams under conditions such that the heat generated during foaming is readily dissipated (e.g.--the foams are a relatively thin cross-section) or under conditions such that relatively little heat is generated during foaming. When polyurethane foams were produced under conditions such that the heat generated during foaming was not readily dissipated, severe foam scorching usually resulted. Later polymer/polyol compositions produced from acrylonitrile-methylmethacrylate mixtures were commercialized and were convertible to polyurethane foams having reduced scorch.
More recently, polymer/polyol compositions produced from polyols and acrylonitrile or acrylonitrile-styrene mixtures have been used commercially. The co-pending Priest application identified herein provides an improved process for forming such polymer/polyols which includes, in general, maintaining a low monomer concentration throughout the reaction mixture during the process. The novel polymer/polyols produced have low viscosities, also the Priest polymer/polyols can be converted to low density, water-blown polyurethane foams having reduced scorch, especially at relatively low acrylonitrile to styrene ratios. However, the stability of the polymer/polyols decreases with increasing styrene-to-acrylonitrile ratios. Further, the discoloration (scorch) of the resulting foams still presents some problems, particularly when the polymer composition contains a relatively high acrylonitrile-to-styrene ratio.
Still further, the co-pending Simroth application which has been identified discloses additional and substantial improvements in forming polymer/polyols. This allows the optimization of the polymer content and the usable monomer ratios for a given polyol in providing satisfactory stable polymer/polyols.
The previously identified Van Cleve et al. application discloses further improvements in the formation of polymer/polyols. As discussed therein, polymer/polyol compositions exhibiting outstanding properties can be made by utilizing, in the formation of the polymer/polyols, a specific type of peroxide catalyst, namely t-alkyl peroxyester catalysts. By the utilization of this specific type of catalyst, polymer/polyols can be produced on a commercial basis with outstanding properties such as filterability in processing, yet which allow either the polymer or the styrene content to be increased. Also, polymer/polyols can be produced on a commercial scale with polyols having a molecular weight lower than have been used prior to this invention.
Despite these improvements, there is still room for further refinement. Commercial production thus requires that the resulting polymer/polyols have relatively low viscosities so that processing in the production equipment can be economically carried out. Further, the stability resulting must be sufficient to allow operation without plugging or fouling of the reactors as well as allowing for relatively long term storage.
The polymer/polyols must also be capable of being processed in the sophisticated foam equipment presently being used. Typically, the prime requirement is that the polymer/polyols possess sufficiently small particles so that filters, pumps and the like do not become plugged or fouled in relatively short periods of time.
While somewhat simplified, the commercial processability of a particular polymer/polyol comes down to its viscosity and stability against phase separation. Lower viscosities are of substantial practical and economic significance due to the ease of pumping and metering as well as ease of mixing during the formation of polyurethanes. Stability is of prime consideration in insuring that the polymer/polyols can be processed in commercial production equipment without the necessity of additional mixing to insure homogeneity.
Accordingly, any improvements which impart more desirable properties to the resulting polyurethanes without increasing viscosity or stability problems would be favorably received. Unfortunately, it has been the experience that increased load-bearing in foams and modulus in elastomers are usually associated with increased viscosity in the polymer/polyol.
It has been theorized that the stability of polymer/polyols requires the presence of a minor amount of a graft copolymer formed from the polymer and polyol. And, a number of literature references have observed large differences in grafting efficiency between the use of peroxides such as benzoyl peroxide and azo-bis-isobutyronitrile in certain monomer-polymer systems while others have noted no marked differences.
In the Journal of Cellular Plastics, March, 1966, entitled "Polymer/Polyols; A New Class of Polyurethane Intermediates" by Kuryla et al., there is reported a series of precipitation experiments run to determine any marked differences in the polymer/polyols produced by either benzoyl peroxide or azo-bis-isobutronitrile when used as the initiators in the in situ polymerization of acrylonitrile in a poly(oxypropylene)triol having a theoretical number average molecular weight of about 3000. The data indicated no significant differences between the polymers isolated, and no marked "initiator effect" was observed.
With regard to addition copolymer stabilizers, efforts in the polymer/polyol field have been concerned with the incorporation of additional amounts of unsaturation to that inherently present in the polyoxyalkylene polyols typically used in forming polymer/polyols. U.S. Pats. Nos. 3,652,639 and 3,323,201 and U.S. Pat. No. 3,850,861 all utilize this approach. The theory is presumably that increased amounts of the stabilizing species will be formed by addition polymerization upon polymerizing whatever ethylenically unsaturated monomers are employed in such polyols.
U.S. Pat. No. 3,850,861 thus discloses the in situ polymerization of ethylenically unsaturated monomers in an unsaturated polyol. Suitable unsaturated polyols are prepared by using an ethylenically unsaturated mono- or polyhydric initiator to form a polyalkylene oxide. The examples set forth include dibasic acids or their derivatives, such as maleic acid. The polyol polymerization medium thus contains one mole of unsaturation per mole of polyol.
U.S. Pat. No. 3,652,639 likewise discloses the in situ polymerization of ethylenically unsaturated monomers in an ethylenically unsaturated polyol medium. The unsaturated polyols of this patent are produced in a manner similar to those of U.S. Pat. No. 3,323,201, as will be discussed hereinafter, except that the level of unsaturation is higher, being on the order of 1 to 3 moles of unsaturation per mole of polyol.
U.S. Pat. No. 3,323,201 discloses a method of preparing a polymer/polyol by the in situ polymerization of ethylenically unsaturated monomers in a polyol having from 0.1 to 0.7 mole of unsaturation per mole of polyol. Unsaturation at the levels set forth in the U.S. Pat. No. 3,652,639 patent were indicated as imparting unnecessarily high viscosities to the resulting polymer/polyols. The unsaturation level that is added can be introduced into the polyol by reacting it with an ethylenically unsaturated compound that is capable of adding to the polyol by reaction with the hydroxyl group, such as maleic anhydride. The polymer/polyols disclosed in U.S. Pat. No. 3,823,201 are asserted to be highly stable due to the presence of the stabilizing species which is formed via the grafting of vinyl polymer chain segments to the unsaturated polyol molecules. Certain improvements in polyurethanes using such polymer/polyols are likewise asserted. More particularly, it is stated that such polymer/polyols are surprisingly superior to those prepared from polyols having high unsaturation in regard to their low viscosities. It is further alleged that polyurethane foams prepared from these graft copolymers exhibit superior load-bearing properties.
A prime difficulty with incorporating additional unsaturation into the polyols such as by the techniques set forth in U.S. Pat. No. 3,652,639 is that an additional step is required and/or processing is made more difficult. The use of maleic anhydride to introduce the additional unsaturation requires an additional step. Moreover, improvements in properties of polyurethanes do not necessarily result; and undesirable increases in viscosity of the polymer/polyol can result.